Transmissively read quad density optical data system

ABSTRACT

An optical data storage and retrieval system using a length of optical recording material in which data in the form of microscopic spots is disposed in cells forming a regularly spaced grid. While the material is being moved in a lengthwise direction by a transport, rows of cells are being read by a linear CCD array, one row at a time. A servo system advances the material so that successive rows can be read, while a second servo adjusts the position of the material in the crosswise direction for proper alignment with the CCD array.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.794,336 filed Nov. 4, 1985, now U.S. Pat. No. 4,634,850, which is acontinuation of application Ser. No. 541,166 filed Oct. 12, 1983, nowabandoned.

BACKGROUND ART

In prior U.S. Pat. No. 4,360,728, assigned to the assignee of the presetinvention, a banking card is disclosed suitable for use with automaticteller machines (ATMs). The patent describes a card having optical datawritten by a laser which forms pits in the medium. The medium itself isdescribed as a thin metallic recording layer made of reflective metal.Types of reflective recording material suitable for use in such cardsare described in U.S. Pat. Nos. 4,269,917; 4,304,848 and 4,363,870, allassigned to the assignee of the present invention. This material ischaracterized by reflective silver particles in a gelatin matrix. Thesilver particles form a reflective field which may be modified by laserwriting or, in some instances, by photographic prerecording ofinformation. Since the material described in the patents is based uponsilver halide emulsions, exposure of data patterns and subsequentdeveloping of the patterns leads to recording of data in a mannersimilar to laser writing. In either case, data is represented by spotsor pits in a reflective field. Reflective spots in an absorptive fieldwould also work.

In many optical data recording and retrieval systems, data has beenrecorded in linear tracks, analogous to magnetic recording. Data is readby following tracks, usually by means of servo systems. Attempts havebeen made to increase the data density of optical storage media withoutincreasing the read error rate. Some lengthwise compression of data hasbeen achieved in both magnetic and optical systems by means of clevermodulation schemes, such as FM and MFM. In U.S. Pat. No. 3,980,818,Browning teaches data storage in a grid of perpendicular contiguousnon-overlapping rows and columns. The data is read with a singledetector in a raster scan-like manner.

In U.S. Pat. No. 4,105,926, Reno et al. teaches a transparent filmcontaining indicia through which a light beam passes. A mirror behindthe film reflects the beam so that it illuminates a small area of thefilm from behind. In the absence of opaque indicia at the illuminatedspot, light is transmitted to a photodetector. The spots represent databits with opaque spots representing ones and transparent spotsrepresenting zeros. In practice, there may be N parallel tracks and Nrespective photodetectors.

Unfortunately, a signal "crosstalk", i.e. detection of unwanted lightfrom adjacent areas around an illuminated spot, often occurs when dataspots and tracks are spaced too closely, due to the fact that some ofthe light from each track reaches photodetectors intended to receivelight from other nearby tracks. In order to reduce crosstalk, theparallel tracks are typically not closely spaced and substantial blankspace is provided between bit positions. Others, such as Browning,sacrifice speed in reading data for higher density by using only asingle detector.

An object of the present invention was to devise a means for formattingoptically recorded data for a data card, or the like, in a way thatincreases data density, while at the same time minimizes error resultingfrom crosstalk and other sources.

DISCLOSURE OF THE INVENTION

The above object has been achieved in an optical data storage andretrieval system in which data is stored in a high density format and isread at a high rate with minimum error. The system includes an opticalstorage medium, such as a data card with a strip of optical data storagematerial disposed thereon, and a linear CCD array. High density isachieved by encoding data as microscopic spots aligned in specified datacell positions of a grid of perpendicular, non-overlapping, rows andcolumns of cell positions.

The optical medium is read transmissively by moving it relative to alinear array of optical detectors. The detector array is disposed forreading on an opposite side of the medium from a light source. Thedetector array is aligned perpendicular to the direction of lengthwisecard motion for simultaneously reading each cell position in a row ofcell positions. A plurality of detector cells read each specified cellposition for minimizing error. Groups of similar cells simultaneouslyread a plurality of specified data cell positions.

Since the linear detector array is perpendicular to the direction ofmotion, there is no need for "track following" in the traditional sense.Data spots are disposed in positions, termed cells, which are rows andcolumns of a regular grid. Each transverse row of cells is usually readmore than one time and these cells must be in alignment with the lineardetector array. Since the entirety of a row is read almostsimultaneously, a new error checking scheme is possible. For example,cells at opposite edges of a row may always have spots, or specifiedspot patterns. Each row of cells contains a discrete set of cells whichcollectively make up usable data. This row can be called a "track". Eachrow is read out by the detector array in parallel with a single scan ofthe contents of the array. The image of the "track" is smaller than thetotal view of the detector array. This allows electronic tracking to beaccomplished with no alignment motion of the card or the electronics.

The card can be moved in (1) an incremental fashion, where the card oroptics is stepped to each new row and the data is recovered, or (2) auniform motion where the electronics continuously reads rows of datauntil a high quality read is found. The electronics can detect a new rowof data by special marks on the ends of the row.

The system minimizes error resulting from crosstalk and other sources byhaving a plurality of detectors of the array observe each data cell.Output from the number of detectors observing a cell can be polled todetermine whether or not a spot existed within a cell. For example, iftwo of three detectors have voltage levels indicative of a spot, thenpresence of the spot is assigned to that particular cell. However, ifonly one detector cell indicates a spot, the cell is determined to beempty. Such polling is also helpful because spots may not be centered ina cell or have a geometrically optimal shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front plan view of an optical data storage and retrievalsystem in accord with the present invention.

FIG. 2 is a frontal blowup view of a data strip having opticallyreadable digital data thereon.

FIG. 3 is a plan view of data spots arranged in cells in accord with thepresent invention.

FIG. 4 is a detail of detector cells aligned for reading data spots inaccord with the present invention.

FIG. 5 is a plan view of data spots in a central band and neighboringbands, with a CCD array spanning the central band and portions of theneighboring bands.

FIG. 6 is a block diagram of optical, mechanical and electricalcomponents of a data strip reader mechanism in accord with the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIG. 1, a card transport 11 is shown. The transportincludes a rail 13 which supports a card 15, such as a credit card. Thetransport 11 includes a readout head 17 mounted for scanning a strip 19carried by card 15. Strip 19 is an optical storage medium, preferably ofthe transmissive type, such as one formed from a silver-halide emulsionwhich has been photolithographically exposed through a mask to actinicradiation and developed to produce a medium with transparent spots in anopaque field. Strip 19 may also be formed from diazo or vesicular typefilms. These materials are commercially available from Xidex Corporationand others. The medium may also be produced with opaque spots in atransmissive field. Other types of reflective or transmissive material,which can support pre-encoded data, formed by laser or other opticaltechniques, such as those previously mentioned in U.S. Pat. Nos.4,269,917; 4,304,848 and 4,363,870, can be used.

The readout head 17 holds a linear array 21 of optical detectors, suchas a CCD array. The linear array has a line of detectors which spans atleast one row of data on strip 19 at a time. Card 15 may have otherindicia thereon, such as alphanumeric indicia 23 serving as eye-readableidentification information. As the card is moved in the direction shownby the arrow A, by an automatic card advancing mechanism, strip 19 movespast the readout head 17 so that the strip 19 passes beneath the lineardetector array 21. This allows microscopic data spots on the strip topass beneath the readout head 17.

FIG. 2 shows a detail of the strip. The card 15 has a strip edge 25 afew millimeters from the upper edge of the card. The optical data stripspans the length of the card, similar to a magnetic data strip on acredit card. Inward from edge 25 is a first data area or band betweenparallel lines 27 and 29. A second data area or band exists betweenlines 29 and 31. The second data area or band is approximately the samesize as the first. The lines 27, 29 and 31 are dark, straight, parallel,spaced apart lines which assist in playback of information. Any numberof such data areas may be disposed on a data strip, depending upon itswidth. The width of each data area is governed by the size and number ofcells disposed across the area. At least one row in one band passesbeneath the readout head. In the case of multiple, parallel bands, thedetector array overlaps bands, as described below. A small quantity ofspots 39 is shown. Here, the spots are disposed in two rows across thefirst data recording area. The spots are microscopic in size, typicallyhave a dimension greater than 3 microns, with the preferred dimensionbeing about 10 microns, and a range of dimensions for an edge ordiameter being between 1 to 35 microns.

The data spots and their positions may be seen in FIG. 3. The dashedhorizontal lines 35 and the dashed vertical lines 37 are imaginary,serving to indicate cells wherein data is written eitherphotographically or by means of a laser. The cells are generally square,although this is not necessary. Within the cells, spots 39 may bepresent or absent. The field in which the spots appear may be opaque.The presence of a spot may increase the transmissivity of the field toan extent that a detector can detect light transmitted through a spotand produce a corresponding signal. Previously described line 29 is seendefining the edge of a recording area.

The spots need not be round, as shown, but may have any regular shape,such as square. There is no required number of cells in a row and norequired numbers of columns of cells between spaced apart parallellines. However, the number of cells in each row is preferably equal.Preferably, the spots are positioned such that they touch each otherwhen adjacent, i.e. contiguous, in lateral and lengthwise directions.

FIG. 4 shows a linear detector array 21 passing over a portion of a gridhaving the data spot 41 within data cell 43. Data cells 45 and 47 areempty, as well as the other data cells which are pictured.

The linear detector array 21 has a plurality of detectors 51, 53, 55disposed for sensing light transmitted to each cell. In this case, threedetectors observe cell 43 and in the process detect spot 41. Since thedetectors are typically CCD devices, the detector output is sensed byshifting charge levels from one end of the linear array to the other.The charge levels are measured in terms of voltages, with a high amountof transmissivity defined as the highest or lowest voltage condition andthe lowest amount of transmissivity defined as the opposite voltagecondition. A threshold level is defined between the maxima and theoutput from the number of detectors observing one cell can be polled todetermine whether or not a spot existed within a cell. For example, iftwo of three detectors have voltage levels indicative of a spot, thenpresence of the spot is assigned to that particular cell. However, ifonly one detector cell indicates a spot, the cell is determined to beempty and the single detector reporting a spot is believed to havedetected foreign material within the cell.

With reference to FIG. 5, a portion of a data card is shown with threeadjacent bands of data spots including central band 38 and neighboringbands 36 and 10. Band 36 is between parallel lines 28 and 30. Band 38 isbetween parallel lines 30 and 32. Band 10 is between parallel lines 32and 34. Each band of data has 46 data cells between the transparentcolumns immediately adjacent to the opaque parallel lines on either sideof a band. The linear detector array 21 has a total of 256 detectorcells uniformly spaced along the array. In reading data the detectorarray is over-filled with more than one band. Approximately one-half ofeach neighboring band 36 and 10 is captured, as well as the entirety ofthe central band 38, which is primarily of interest. The linear detectorarray is preferably read several times so that ambiguities may beresolved by comparing successive reads of the same row. This isdescribed further below. The central band 38 may be followedelectronically by identification of the parallel lines 30 and 32, eachhaving white, i.e. transparent, columns on either side of the line, suchas the columns 42 and 44 and data bits forming track marks at the end ofeach row. The track marks may indicate track numbers so that the addressof each track is established. Once a band is read, such as band 38, thecard, or the optics disposed above the card may be moved so that thenext band of data may be read. This constitutes electronic tracking ofdata with very fine separation of relevant data from other data ornon-data areas of the card.

With reference to FIG. 6, an optical data storage medium 46 is shown tobe supported in a card transport 11 driven by a motor 57 via a belt 48.The card is held firmly in place by guides 13, seen in FIG. 1, servingto locate edges of the card. Motor 57 may be a stepper motor undercontrol of motor servo 59. The transport is capable of moving card 46back and forth, with extreme positions of the transport signaled byoptical limits 61 which are electrically connected to motor servo 59.

A beam source, such as a laser 40, generates a radiation beam 49directed toward the data bands on card 46 by means of optics 63typically a focusing lens. Light transmitted through the card isdirected toward a linear detector array 50 by means of a lens 52. Lightsource 40 and detector 50 are mounted on opposite sides of the card on amovable support 54 which is driven by a motor 56. Light source 40 is asemiconductor laser operating at infrared wavelengths. The motor is astepper motor which is controlled by a second motor servo 58. Both thefirst motor servo 59 and the second motor servo 58 are connected to adata bus 80 for computer control. The first servo 59 forces motor 57 toadvance card 46 in a lengthwise direction so that successive rows ofdata may be read by the linear array 50. On the other hand, steppermotor 58 provides crosswise motion control so that various bands of datamay be read.

The linear array 50 is able to read successive rows of data,asynchronously scanning the data, in a sense, as the data is shifted outof the linear array. The start of each scan is indicated by means of astart pulse. As previously mentioned, a CCD driver 60 receives incomingdata bits along line 62 and produces a start pulse along line 64 oncethe start of data is recognized. Since the data is self-clocking, clockpulses may be generated from the data stream arriving on line 62 andthese clock pulses are sent to other system components along line 66.Undecoded data is transmitted along line 68 to a data decoder circuit 70having memory with various data patterns. Clock pulses provide timingmarks so that data patterns may be recognized. Data is also transferredto a reference line follower circuit 72 which recognizes the lines whichmark the edges of each band. One of the data patterns to be decodedconsists of track marks on the card. Such marks are embedded in each rowwhich, as previously indicated, is termed a "track". Reference lineinformation is transmitted from reference line follower 72 to decodercircuit 70 so that track marks can be located adjacent to the referencelines. The memory of the bit decoder 70 contains a map indicating wheredata should be expected. A counter in the bit decoder cooperates withthe map in order to match the data stream along line 68 to decoded databits.

The linear array 50 is clocked at a rate so that each row of data isread at least a few times before the optics passes on to the next row.Each scan from the linear array is tested to find out if it is a newtrack. If it is a new track, then the best previous pattern match fromthe previous track is transferred to the data bus. Other scans from theprevious track are discarded. Each scan of the same track is compared tothe previous best decoded track until the best data pattern for that rowhas been selected when the next row scan is initiated. The best row ismeasured by reading track marks at the end of each row. Each track alsomay be checked for parity. Decoded data is transmitted to a line buffer74 which converts data to parallel bytes for transmission to bus 80. Acomputer is connected to the data bus for testing data as describedabove and for providing error correction. The computer also providescontrol for the motor servos 59 and 58 using known servo correction andfeedback techniques.

As previously mentioned, each card carries opaque, straight, parallelreference lines separating bands of data. After a band has been read,the second servo 58 positions the optics for reading the next band.Instead of moving the optics, the card could have been moved in thecrosswise direction.

In the present invention, the motors 56 and 57 provide coarsepositioning of the card so that the linear array can scan a row ofcells, plus neighboring cells on either side of the row. The CCD arrayseparates the row utilizing the track marks within each row and in thismanner performs electronic tracking of the data. This may be consideredto be fine tracking of the data which cooperates with the coarsetracking.

While the preferred embodiment has described a card having a strip ofopaque material with transparent spots thereon, it will be realized thata continuous strip could be wound on hubs, like tape. Moreover, thematerial need not be opaque with transmissive spots but could betransmissive with opaque spots or reflective. Reflective material wouldbe read by light reflecting from the material onto a detector array onthe same side of the material relative to the source. The material neednot be a film material. Most types of laser data storage media can beused.

What is claimed is:
 1. An optical data storage and retrieval systemcomprising,an optical data storage medium having optically readabledigital data encoded by microscopic spots in specified data cellpositions on said medium thereby changing transmissivity of the medium,said data cell positions forming a grid with perpendicular, contiguousyet non-overlapping rows and columns of cell positions, said columnsaligned with the length of said medium, and a linear CCD array alignedperpendicular to said columns of cell positions on a side of said mediumopposite a light source, said array having a plurality of fixed positiondetector cells imaging each specified data cell position in a row ofcells, wherein at least two detector cells image a specified data cellposition, with groups of detector cells simultaneously imaging aplurality of cell positions.
 2. The system of claim 1 wherein saidstorage medium comprises a strip of opaque optical data storage materialwith transparent microscopic spots.
 3. The system of claim 2 whereinsaid strip of optical data storage material is mounted on a wallet-sizecard.
 4. The system of claim 1 wherein a first group of rows isseparated from a second group of rows by a lengthwise opticallyabsorptive line.
 5. The system of claim 1 further comprising a firstservo for adjusting the crosswise position of the storage mediumrelative to the CCD array.
 6. The system of claim 5 further comprising asecond servo for incrementally advancing the lengthwise position of thestorage medium.
 7. An optical data storage and retrieval systemcomprising,a data card having a length and a width with a strip of anoptical recording medium thereon, said strip having microscopic dataspots aligned in contiguous data cell positions forming a grid withnon-overlapping elements in said lengthwise and widthwise directions, adata readout head having a linear photodetector cell array disposed on aside of said data card opposite a light source to transmissively readdata spots on the strip in a direction across the width of said card,wherein said readout head has a plurality of detector cells of saidlinear detector cell array for each cell position in a row of cellpositions, with groups of detector cells simultaneously imaging aplurality of cell positions and card transport means for advancing saidcard relative to said head in a direction parallel to the length of saidcard.
 8. The system of claim 7 further comprising a second servo foradjusting the crosswise position of the medium relative to the CCDarray.
 9. A data card read system comprising,a data card havingcontacting, yet non-overlapping parallel rows of data cells arranged ingroups of contacting parallel columns, each data cell capable of holdinga single bit of data approximately the size of a laser beam diameter,each group of columns of data cells spaced from a neighboring group ofcolumns, thereby forming parallel bands of data, a card transport havingmeans for moving the card, a beam source means for directing a radiationbeam onto the card and beam detector means on an opposite side of saiddata card from said beam source means for reading said radiation beamafter transmission through the card, said beam detector means capable ofsimultaneously reading a row of data cells, wherein said beam detectormeans include a linear array of fixed position detectors, wherein atleast two detectors read each data cell, with groups of detector cellssimultaneously imaging a plurality of cell positions, and card transportmeans for advancing the card relative to the beam source and the beamdetector means so that successive rows of data can be read.
 10. Theapparatus of claim 9 wherein parallel bands of data are separated byparallel, absorptive lines.
 11. The apparatus of claim 9 wherein eachrow of data cells has track marks at opposed ends, said track marksidentifying a row.
 12. The apparatus of claim 9 wherein said detectormeans comprises a linear array having a width greater than a row ofdata, said linear array having detector cells imaging data in a row plussome data from rows in neighboring bands.
 13. A data card comprising,asubstrate capable of supporting an optical data storage medium, and anelongated data storage medium on the substrate having a rectangularnon-overlapping array of contiguous storage cells, including a lengthdimension and a width dimension, some of the storage cells having dataspots therein of microscopic size, the remaining storage cells beingempty, said spots being mainly transmissive of light in comparison tothe surrounding field which is mainly opaque to light, the data beingarranged in tracks along the widthwise direction, at least one end ofeach track having spots marking the presence of the track, each of thestorage cells in a track having a size capable of being imaged by aplurality of adjacent detector cells in a linear array.
 14. The datacard of claim 13 wherein said rectangular array of storage cells isdivided into a plurality of bands by parallel, absorptive lines, eachband containing a plurality of tracks.
 15. The data card of claim 13wherein the size of said spots is between 1 to 35 microns along an edgeor a diameter.
 16. The data card of claim 13 wherein at least some ofsaid data spots are contiguous in both lengthwise and widthwisedirections.
 17. The data card of claim 13 wherein said spots arephotographically prerecorded in a photosensitive emulsion having anoptically contrasting field surrounding the spots, said emulsion formingsaid storage medium.